Traffic transportation signaling system



Dec? 1944. E w. KELLOGG ET AL 4 TRAFFIC TRANSPORTATION SIGNALING SYSTEMFiled April 29, 1942 Enventors Gttorneg Patented Dec. 19, 1944 PAT ENTSOFFICE zsssu TRAFFIC TRANSPORTATION SIGNALING SYSTEM Edward W. Kelloggand Glenn L. DimmickQIn dianapolis, Ind., assignors to Radio Corporationof America.

a corporation of Delaware Application April 29, 1942, Serial No. 440,9241 Claim. 177-329) This invention relates to traflic signaling systemsand more particularly to railway signaling lights used for informingtrairimen of the condi- .tion of the railroad ahead.

Heretofore, in railway signal lights, used for informing the engineerwhether he should proceed, slow down, or stop, etc., considerabledifflculty has been encountered because of the fact that sunlight, undercertain conditions, has been reflected from within the signal lights,giving a false signal. In a certain angular range between the light raysfrom the sun to the signal light and the line of view of the observer,the sun's rays have caused apparent illumination, the same as thatcaused by the incandescent signal lamp. The uncolored reflected sunlightis not serious,

filament 8 located in the center of the lamp bulb. Light rays 8 from thelamp filament are refracted by the lenses I and 2, as indicated for aportion of the system, to ,form a substantially parallel beamemerging'from the lenses, as shown at 9. Light from a distant source,such as the sun, coming from the opposite direction, and striking thelenses, is caused to converge to the filamentas may be illustrated bythe lines representing the although it tends to blind the observer tothe true I signal. However, some of the sunlight is reflected afterpassing through the colored glass.

This effect has been known as a "false clear" and has been the cause ofmany serious accidents. This trouble has persisted for many yearswithout apparently any solution.

An object of our invention is to provide a signal light that is free offalse clear signals caused by light from an external source, such as thesun.

,We discovered that the trouble was caused by light from the sun,transmitted through the lenses, striking th surfaces of the lamp bulb,and being -reflected out again as colored light through the lenses,thereby giving the false clear" signal. This observation was proven bythe fact that when the signal lamp within the optical structure wascompletely removed, the troublesome reflected light was reduced to anegligible quantity.

The invention will be described herein in connection with a railwaysignaling system of the type above referred to, and its scope will bepointed out in the appended claim. For a further consideration of theinvention, attention is now directed to the following description inconnection with the accompanying drawing, in which Figure 1 is a sideplan view, in section, diagrammatically representing the major portionsof a conventional railway signaling lamp and optical system, embodying aspecies of the invention, Figure 2 is a side view, partly in crosssection, of a railway lamp optical system and our improved lampembodying the preferred form of the invention.

Referring to Figure l, we have illustrated a conventional railwaysignaling optical system consisting of a colored glass Fresnel lens Iand clear glass lens 2 to the rear of which lenses is located aspherical shaped lamp bulb 4 having a outgoing light rays 9 and 8 abovediscussed. It is apparent that rays reflected from the spherical bulb,at both the outer and innerforward surfaces at I 0 and from the innerand outer rear surfaces at i2, are directed back over their same pathand leave the lenses as substantially a parallel beam, illustrated at 9.

We found that if the outside surface of the lamp was coated with asuitable material, the reflected light was greatly reduced, as is knownin the art. Coating or otherwise treating of the outer surface, only, ofthe lamp was found to reduce the light reflected to about 50 percent,but

this amount was not suiiicient because to the eye I it was not a verylarge reduction. Coating the but it is quite a problem outside is quitepractical with the existing bulbs, to construct a lamp with the insidesurface coated, as would be necessary for a more substantial reduction.method of coating or treating the glass surface may be used. See, forexample, F. H. Nicoll "A new chemical method of reducing reflectance ofglass in RCA Review, January, 1942, and K. B; Blodgett Physical Review55, page391 to 404 of February 15', 1939.

The reflection-reducing expedient previously referred to has theproperty of producing minimum reflection at a certain wave length.Incidentally, the transmission of light is most efficient at the samewave-length. It is possible in a modiflcation of the above-mentionedprocess to reduce reflection to a lower value at the minimum point ifsome increase in reflection at other wave lengths may be tolerated. Inthe present application it is particularly important that reflection ofgreen light from the green signal and red light from the red signal bereduced to minimum.

Referring to Figure 2, there is'illustrated the same optical system,including lenses I and 2, but with a lamp 1 having a. diflerent andnon-spherical contour bulb or envelope, and a filament 6 or other sourceof light therein. In accordance with our invention, we have designed theshape of the bulb such that for all incoming light beams 9 and 8striking the forward surfaces around In and the rear surfaces around l2,the light beams Any suitable 8 and I6 travel in a in Figure 1.

' and the corresponding predetermined ray ii and it are reiiected 1mmand converse at, or near, some an- Platerallyofihelampandat such alocation, e. 2., the inside wall of the housreflected the lenses. The rrays ll direction outside the conical angle formed between the filamentand outer periphery of lens i and fall, preferably, on light absorbingor dissipltini surface, or surfaces, thereby preventing a re-reilecflon.These reflected rays are thus prevented from returning along theiroriginal path a to an observer, and the signal lamp appears practicallydark, although the suns rays fall upon its surfaces as indicated by rays8. we have, therefore, by this arrangement, eliminated the false clear"signal. The outwardly projected useful rays from filament i follow thepaths 8 and 9 as usual, the filament being located in the same positionrelative to the lenses as that We have-shown the light rays for oneportion of the system, but the same applies to other portions.

In Figure 2 the design of the glass envelope enclosing the filamentarylight source is such that the forward portion around II is approximatelyconical, or convex-conical, and makes a sumciently acute angle, orangles, with respect to the axis of rotation that radial rays passingrrom any part of lens 1 toward the filament will not strike any surfaceof said forward lamp portion normally thereto. In connection with thisdesign, the tip of the bulb is preferably closely adjacent lens 1|. Theshape or the forward portion of the envelope is such that the incoming,or incident rays, will be reflected laterally to some region back of thelens system. The shape is derived by bisecting the angle between any rayI groups ll or I i, and making the envelope normal to the bisecting lineat the point or intersection. The rear portion ll of the envelope ismore curved than the forward portion and, as shown, the reflected lightwill converge at P. However, it is not essential that it converge at thesame line P, as do the rays from portion II. In fact, the-rear portionII can be shaped more like the forward portion II, and the reflectedrays will cover an area to the rear of P along the housing side wallsFor want or a better term. we refer to the go raysdonotpassout thesesurfaces, re- A substantially the position illustrated preferred onedepartures may be made from the particular form illustrated withoutdeparting from our invention. a

As an initial practical demonstration of the principle involved in ourinvention, we obtained a lamp bulb which has a shape approaching thatillustrated in Figure 2, approximately resembling an egg or a pear incontour, and when placed in for operation, and compared with theoriginal. spherical lamp shown in Figure 1, it was found to be effectivein reducing the reflected light to a negligible value in spite of thefact that the shape or this bulb was not ideal.

We have, therefore, provided two ways of solving the false clear signalproblem: (a). by applying light reflection reducing coatings to thepresent spherical bulbs used in railway signal lamps, and (b) providinga signal lamp bulb with such a shape and location that the reflectedlight caused to travel 1 in a path other than that which would cause an1 from an external source will be vention, except as limited by thefollowing claim. 7

Having thus described our invention, what we claim as new is:

In an optical signaling system, a lamp envelope containing a source oflight, a retracting lens for projecting light from said source outwardlyfrom said system, and a substantially non-reflecting transparent coatingon said lamp envelope for reducing the reflection of external lightentering said system while offering substantially no obstruction to thepassage of said light from said source, said lens and said coating beingcharacterized by the fact that the former transmiis light of apredetermined color and the latter minimizes reflection of light of asimilar color. EDWARD W. KELLOGG. GLENN L. DIMMICK.

lamp bulb g all as a: share. and particularly as convex-conical at eachend. Vari-

